It is known in the art to provide an article such as an automotive windshield or the like, with a profile bead of a polymeric material around the peripheral edge of the article. A profile is often molded or otherwise fabricated, cured and adhesively bonded to the peripheral edge of the article. U.S. Pat. No. 5,108,526, for instance, discloses a method of forming a profile onto such an article by extruding a profile material directly to the peripheral edge thereof by use of a die head that can circumferentially traverse the peripheral edge of the article. The profile material is viscous and can be cured after being extruded. Profile materials are known which may air-cure such as by absorbing moisture or by the application of heat or the like.
With devices to extrude the profile material directly onto the peripheral edge of an article, it is known that it is difficult to extrude the profile uniformly around corners, bends, turns and the like. The die head is typically fitted with a die plate having an extrusion profile orifice therein. The orifice is normally positioned generally orthogonally to the peripheral edge of the article. Hence, when the die head is moved around a corner, the inside of the orifice moves at a slower rate than the outside of the orifice. By "inside" it is meant in a more proximate position to the article than the "outside" or more distal portion of the orifice.
Because the inside of the orifice moves at a slower rate than the outside of the orifice at the corners or bends of the article, a constant flow rate of profile material to the orifice will result in the deposition of more profile material at the inside of the orifice than at the outside. Accordingly, the profiles have non-uniform cross-sections between linear sections of the article and the corners thereof.
One proposed solution to this problem has been to adjust the total amount of material directed to the orifice. By pumping less material to the orifice, the inside section of the profile would not become too thick. However, the outside of the profile in the corner areas was then too thin and the problem of non-uniform cross-section remained.
Another proposed solution, which is disclosed for example in U.S. Pat. No. 5,108,526, was to provide two or more supply channels to the profile orifice, one generally positioned to supply the inside of the profile orifice and one to supply the outside of the orifice. One of the supply channels was then provided with a means for selectively restricting the flow of material therein, such that the portion of the profile adjacent thereto could be made thinner or thicker by adjusting the amount of material delivered to the respective portion of the orifice. The volume of the material delivered to the orifice was thus regulated.
It was found that the restrictively regulated flow channels still provided profiles of varying cross section. For example, it is stated in the '526 patent that thinner and thicker cross sections are selectively provided therein. Also, it has been found with devices such as that of the '526 patent, that when the separate channels were merged just prior to the orifice the benefits and effectiveness of the separate channels was lost.
Another drawback found to restrictively controlling flow in a flow channel, was that the total restriction of the flow within the nozzle was simultaneously varied as well. This was found to cause irregularities in the total flow at the nozzle due to the compressibility of the material and expansion capacity of the ducts connecting the material supply to the nozzle. The additional total increase in friction to the flow was found to additionally affect the delivery rate of material from the supply thereof.
A need exists therefore, for an apparatus for extruding a profile onto the peripheral edge of an article, wherein the cross section of the profile remains substantially constant throughout a linear section and a corner section of the article.